الفهرس 
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Abstract
The present study aimed to determine the microcrack incidence during root canal preparation by AF blue and RECIPROC blue files using stereomicroscope and to evaluate the cleaning action of AF blue and RECIPROC blue files to remove smear layer using Scanning-Electron Microscope.
This study was conducted on 60 Disto-buccal root canals of extracted human permanent maxillary molars. Only maxillary molars with non-fused roots and separate distobuccal canals with root curvature ranged from 10-25° were selected.
The curvature was evaluated according to Schneider’s method where teeth were radiographed first to assess canal morphology (Schneider, 1971). Access cavities were prepared with round bur and Endo-Access bur.
All teeth were decoronated at right angles to the vertical axis at 3 mm above the proximal cemento-enamel junction to ensure standardization and straight-line access using a diamond bur accompanied with water cooling. The mesial and palatal roots with the respective part of the crown were sectioned. Lengths of the remaining roots were standardized to be 12 mm, then the distobuccal roots are resected using a diamond disc. The teeth were then cleaned and stored in distilled water until the time of use. Only the distobuccal canal has been prepared.
Roots were fixed into elastomeric impression material and acrylic resin mold to imitate the periodontal ligament (Pedullà et al., 2017). The apical 4 mm of the roots was exposed to allow intraoperative image recordings.
Randomization of the 60 samples was done and divided equally into 2 groups (n = 30) which would be subjected to mechanical preparation using the following instrumentation systems.
group 1: AF blue 25#6.
group 2: RECIPROC BLUE R25.
After preparation, each group has been subdivided into two equal subgroups each with 15 samples according to the evaluation method:
Subgroup A: tested for the presence of dentin micro-cracks. The sectioned root is inspected first for the presence of any previous cracks using microscope. Microscopic evaluation:
1: Stereomicroscope:
Sections were then viewed under a stereomicroscope. The apical third of the distobuccal root have been examined before and after preparation at 40x. Images were captured using a smart phone camera for evaluation of dentinal defects.
One mm of the apical portion of each tooth are ground perpendicular to the tooth axis with waterproof 320-grit silicon carbide abrasive paper. The apical surface is then polished with waterproof 1,000-grit and 1,200-grit silicon carbide abrasive paper to reduce the fine scratches and to obtain a clear, highly magnified image.
Two examiners independently and blindly scored the images of apical third of the canal and Root cracks have been divided into two categories:
• No defect: Root dentin is devoid of any craze lines or cracks (score 0)
• Defect:
- A craze line: a line extending from the outer surface into the dentin but will not reach the canal lumen. (score1)
- A partial crack: a line extending from the canal walls into the dentin without reaching the outer surface. (Score 2)
- A fracture: a line extending from the root canal space all the way to the outer surface of the root. (Score 3)
2: Scanning electron microscope:
The samples were managed and observed with SEM for evaluation of the smear layer. Representative sections at a magnification of 2,000× for smear layer at the apical third of the canal were used. The images of the most representative area were saved digitally. The cleaning ability of the file was evaluated using the debris and smear layer scoring system introduced by Hulsmann et al. Two examiners independently and blindly scored the images of apical third of the canal. The examiners were originally adjusted to the Hulsmann scoring system;
Score 1: No smear layer, dentinal tubules open.
Score 2: Small amount of smear layer, some dentinal tubules open.
Score 3: Homogenous smear layer covering the root canal wall, only few dentinal tubules open.
Score 4: Complete root canal wall covered by a homogenous smear layer, no open dentinal tubules.
Score 5: Heavy, non-homogenous smear layer covering the complete root canal wall.
The collected data were recorded, tabulated, and subjected to statistical analysis by using Mann-Whitney statistical test.